Sana, Yemen - President Ali Abdullah Saleh of Yemen said Wednesday that he would not run for re-election when his term ends in 2013. The announcement was a stunning concession to protesters and another reverberation of the popular anger that has rocked the Arab world in recent weeks.

Mr. Saleh, an American ally who has been in office for 32 years, said that his eldest son, Ahmed, who heads the elite Republican Guard, would not seek the presidency either. Opponents of the government had feared that Mr. Saleh would try to pass power to his son.

The announcement came a day before planned protests in Sana, the capital, and other districts in Yemen. Last week, the country witnessed the largest demonstrations of Mr. Saleh’s tenure, and organizers said they expected an even higher turnout on Thursday.

Yet even as opposition leaders met to prepare their official response to the president’s announcement, the government moved to try to stage-manage Thursday’s events by helping rural Yemenis from the outskirts of Sana, the capital, and from the pro-Saleh province of Khowlan to travel to the city for counterprotests. About 500 pro-government people had already gathered in a central square in Sana on Wednesday, setting up large white tents with the intention of holding the square through the night.

The president’s announcement came a day after President Hosni Mubarak of Eygpt, in the face of a protest that gathered hundreds of thousands in downtown Cairo, declared that he would step down in September after finishing his term.

“No extension, no inheritance, no resetting the clock,” Mr. Saleh said Wednesday in a joint session of Parliament and another legislative body that was boycotted by the opposition. “I present these concessions in the interests of the country. The interests of the country come before our personal interests.”

The president urged the opposition to cancel their planned demonstrations, and he invited them to resume a dialogue that collapsed last October after the government announced plans to hold parliamentary elections in April, before opposing political camps finished their deliberations.

In another concession, Mr. Saleh said Wednesday that he would delay the parliamentary elections until better voter records could be compiled, as the opposition has demanded.

The concessions were met with skepticism by opposition lawmakers, an eclectic group dominated by Islamists. Several opposition lawmakers said they would go ahead with their plans for protests on Thursday and said they were concerned that Mr. Saleh would not follow through on his promises.

In 2005, Mr. Saleh announced that he would not seek another term, only to change his mind a year later. He was elected in 2006 to a seven-year term.

“We lost confidence in the president,” said Zaid al-Shami, a lawmaker and opposition figure. “It is not the first time he promises something that he ends up not honoring.”

Unlike the protesters in Tunisia and Egypt, who called for the immediate ouster of their countries’ presidents, Yemeni protesters are asking for reforms and a smooth transition of power through elections. Mr. Saleh’s promised concessions marked another acceleration in the momentum that has gathered across North Africa and the Middle East for deep, even radical, change in a longstanding regional order backed by the United States.

On the streets of Sana on Wednesday, many people seemed to support the president’s decision, though they were wary of his reasoning. “When the next elections come, change is necessary,” said Ahmed Shelaly, 41, who works as a taxi driver and as the media director for a local nonprofit group. The president decided not to run out of fear, Mr. Shelaly said. “He’s scared because of Egypt, and people here have weapons, much more so than Egypt.”

Yemen, the poorest Arab country, is troubled by a rebellion in the north and a struggle for secession in the formerly independent south. In recent years, an affiliate of Al Qaeda has turned parts of the country into a refuge beyond the state’s reach. A remarkably high proportion of citizens are armed.

In another gesture that he portrayed as an act of good will, Mr. Saleh ordered the creation of a fund to employ university graduates and to extend social security coverage. He also increased wages and lowered income taxes.

Though most opponents were wary of the president’s statements, some called them positive and said that if they are realized, they would allow for a peaceful change of power.

“As long as we have started, we are on the right track for democracy,” said Sheikh Mohammed Abulahoum, a prominent tribal leader and politician. “This way, it will be a safe, secure and permanent transition of power, without casualties, and a low cost.”

The country’s stability has been of increasing concern to the United States, which has provided $250 million in military aid in the past five years. Secretary of State Hillary Rodham Clinton, on a visit to Sana in January, urged Mr. Saleh to establish a new dialogue with the opposition, saying it would help to stabilize the country.

Previously, Mr. Saleh had offered some political concessions and promised to raise salaries for civil servants and the military, in a country where many people live on less than $2 a day.

On Tuesday, for instance, the state news agency, Saba, reported that the president had ordered retailers to stop charging the military and security forces for food and gasoline.

The Yemeni opposition had promised to call a demonstration every Thursday until March, when it will evaluate whether its demands have been met.

Yemen shares a desert border with Saudi Arabia, the oil-rich United States ally that has so far shown no sign of the popular pressures sweeping through less prosperous lands like Yemen and Jordan, where the king dismissed the cabinet on Tuesday in response to protests.

And in Syria, calls for a “day of rage” this weekend against the government of President Bashar al-Assad were spreading on Facebook, which is formally banned in the country, and on Twitter.